On 17.01.24 17:54, Rob Herring wrote:
On Wed, Jan 17, 2024 at 8:02 AM Alexander Graf <graf@xxxxxxxxxx> wrote:
On 03.01.24 19:48, Rob Herring wrote:
On Fri, Dec 22, 2023 at 12:52 PM Alexander Graf <graf@xxxxxxxxxx> wrote:
With KHO in place, let's add documentation that describes what it is and
how to use it.
Signed-off-by: Alexander Graf <graf@xxxxxxxxxx>
---
Documentation/kho/concepts.rst | 88 ++++++++++++++++++++++++++++++++
Documentation/kho/index.rst | 19 +++++++
Documentation/kho/usage.rst | 57 +++++++++++++++++++++
Documentation/subsystem-apis.rst | 1 +
4 files changed, 165 insertions(+)
create mode 100644 Documentation/kho/concepts.rst
create mode 100644 Documentation/kho/index.rst
create mode 100644 Documentation/kho/usage.rst
diff --git a/Documentation/kho/concepts.rst b/Documentation/kho/concepts.rst
new file mode 100644
index 000000000000..8e4fe8c57865
--- /dev/null
+++ b/Documentation/kho/concepts.rst
@@ -0,0 +1,88 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+=======================
+Kexec Handover Concepts
+=======================
+
+Kexec HandOver (KHO) is a mechanism that allows Linux to preserve state -
+arbitrary properties as well as memory locations - across kexec.
+
+It introduces multiple concepts:
+
+KHO Device Tree
+---------------
+
+Every KHO kexec carries a KHO specific flattened device tree blob that
+describes the state of the system. Device drivers can register to KHO to
+serialize their state before kexec. After KHO, device drivers can read
+the device tree and extract previous state.
Can you avoid calling anything "device tree" as much as possible. We
can't avoid the format is FDT/DTB, but otherwise none of this is
Devicetree as most folks know it. Sure, there can be trees of devices
which are not Devicetree, but this is neither. You could have used
BSON or any hierarchical key-value pair serialization format just as
easily (if we already had a parser in the kernel).
I understand and agree - it's been confusing to pretty much everyone who
was looking at KHO so far. Unfortunately I'm terrible at naming. Do you
happen to have a good suggestion? :)
How does this work with kexec when there is also the FDT for the h/w?
The h/w FDT has a /chosen property pointing to this FDT blob?
Yep, exactly.
Those properties need to be documented here[1].
Oooh, thanks a lot for the pointer! I'll add them :)
Alex
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